The inspiration for this shot comes from the social media craze of "tiny planet photos", and is created using a 360-degree camera (in this case, the GoPro Fusion, which hadn't been released at the time of filming) and manipulating the video file in post-production.
In addition to tourists visiting for the U-Drop Inn, Shamrock is known throughout the state for it's St. Patrick's Day celebration - which has been designated as the official St. Patrick's Day celebration for the state of Texas.
Shamrock has a total population of ~1,870, which makes it's 20,000+ tourists per year over 10 tourists per resident. By way of comparison, Croatia is the most over-touristed country in the world with 14 tourists per resident, and substantially above many major US cities.
Ken and Brian are laughing because the fire button does not start the car - it activates the fire suppression systems, which happened by accident during a photo shoot with Ken's Ford Escort Mk 2.
A "double A" references the Ford Model AA, which was the truck variant of the Model A, the successor to the Model T. A variety of specialty body types were available, including dump trucks, ambulances and funeral coaches.